A variety of surveying and paralleling instruments are widely used in the art of preparing dental restorations, such as removable and fixed bridges and dentures, from dental models of the teeth of the recipient. Thus, for example, dental surveyors are used to determine the largest contours of those viable teeth to which a denture will be anchored. Generally, anchoring clasps are placed just below the line of the largest coutour. Also, dental surveyors are used for wax relief of undercut areas of abutment teeth and to locate paths of insertion. Paralleling insturmentation is also used in the precision dowel pin technique in the manufacture of dentures and bridgework. Paralleling instrumentation may also be used in a variety of other grinding, milling, drilling and parallel pin work operations. In all of these applications it is highly desirable for accuracy that the tool contacting or operating upon the dental model always remain oriented in the vertical direction as it passes from point to point upon the dental model.
One class of prior art dental surveyor is the hinged arm surveyor. This type of surveyor comprises a vertical support and a horizontal hinged arm extending from the support and holding a surveying tool at its end. Rotation of the horizontal arm about the axis of the vertical support, combined with elbow-like relative rotation of the two components of the horizontal arm, allows for movement of the tool upon the dental mode. However, because the two components of the moving hinged arm must remain in perfect horizontal alignment in order to maintain the vertical alignment of the tool, the hinged arm must be bulky in construction. Thus, this type of instrument tends to respond heavily and somewhat sluggishly to the touch of the operator using it.
Another type of prior art dental paralleling instrument is the Austenal Micro-Analyzer (Howmedica Inc., Dental Division, Chicago, Illinois). This instrument comprises a vertical support, a horizontal cantilever extending therefrom, with the cantilever being rotatable about the axis of the vertical support, and a tool bar which is horizontally slidable within the cantilever. The rotation of the horizontal cantilever about the vertical support, combined with the horizontal sliding of the tool bar within the cantilever, provides for full movement of the vertically oriented tool upon the dental mode. This surveyor is capable of producing highly accurate work and has achieved considerable acceptance in the art. However, because the horizontal cantilever must remain in precise horizontal orientation and also serve as a moving part, a heavy construction is necessary and the response of this type of surveyor to the touch of the operator is not as light as would be desired.